Erratic proximity polling by a mobile Mine
From Worms Knowledge Base
When a Mine checks for nearby worms to see if it should arm itself, it does not check every frame (1/50th of a second) to minimize extra calculations per second for the game. Instead, it only checks for them every 1/5th of a second.
If a mine is stationary, but a worm on a Ninja Rope is moving at maximum speed and swings close to the mine, the worm may completely pass through the mine's detection range during the frames that it is not checking for nearby worms. It is also possible to Fire Punch a mine without triggering it. Of course, this trick requires a large amount of luck to successfully work. It will only work if the mine is near the worm during the frames that the mine is not checking for nearby worms, which is nearly impossible to judge.
A bug, fixed in W:A v22.214.171.124, caused moving mines to poll for nearby worms erratically; much more than 1/5th of a second could go by with no polling being done. (Ironically, the bug was created by code that was meant to speed up the proximity polling on a moving mine.) In versions of Worms with this bug (including Worms2 and WWP), a mine knocked by an explosion, dropped from a large height, or moved in other ways could easily pass near a worm without being triggered.
In W:A v126.96.36.199 and later, a moving mine polls more rapidly the faster it is moving, up to a certain speed where it polls every 1/50th of a second. (This is what was originally intended.) This makes it very unlikely that a moving mine will pass close to a stationary worm without being triggered.